Guitar magnetic microphone



H. DE ARMOND GUITAR MAGNETIC MICROPHONE Nov. 30, 1948.

Filed March 20, 1946 INVENTOR.

Patented Nov. 30, 1948 OFFICE GUITAR MAGNETIC MICROPHONE Harry De Armond, Toledo, Ohio, assignor to Rowe Industries, Toledo, Ohio Application March 20, 1946, Serial No. 655,759

provide an electromagnetic pick up device of the type indicated which will amplify the several varying types of strings used on such an instrument in a more or less equal manner so that the tone produced by one string is not amplified more than those produced by others. More specifically, an object of the present invention is to provide a special arrangement of the magnets of the elec tromagnetic pick up device so arranged with rela- 3 Claims. (Cl. 84-1.16)

tion to the several strings of the instruments as to accomplish the uniform amplification referred to.

A further object is to provide a correlation of magnets, pol-e pieces, windings; supporting casin and unique assembly thereof to produce an improved pick up greatly improving the tone quality and uniformity of the amplified notes produced by' the instrument.

Further objects and advantages are within the scope of the invention such as relate to arra ment, operation, and function of the related elemen-ts of the structure, to various details of con struction and to combinations of parts, elements per se, and to economics of manufacture and numerous other features as will be apparent from a consideration of the specification and drawing of a form of the invention, which may be preferred in which:

Figure I is a plane view showing the application of the pick up to a six-stringed guitar;

Figure II is a top plane view on an enlarged scale of the pick up showing its relation with respect to the strings of the instrument;

Figure III is a similar view with the cover of the pick up removed;

Figure IV is a longitudinal, sectional view taken on the line I'V-IV of Figure III;

Figure V is a cross sectional View taken on the line VV of Figure III; Figure VI shows a modified magnet.

Referring to the drawings, the invention may be applied to various types of stringed instruments, but I have here shown it applied to the body of a guitar as indicated at H) having the usual type of tail piece l2 to which the several strings are connected. The usual type of bridge 14 is illustrated and a form of pick guard i is shown located as it is usually arranged along side the first string.

' My electromagnetic pick up is designated generally by numeral and is thin enough to be inserted between the strings and the guitar body In.

It is understood that wires 2| are connected to the pick up 20 in and led to a suitable amplifier not shown. As indicated, the pick up 20 may have one end closed rounded as at 22 and the other end 23 squared off in relation to the sides so that the device may fit as closely as possible to the pick guard i5 at this end. A short lateral extension it receives the terminal for the wires 2 5.

One of the most important features of my invention is the arrangement of the magnets, the production of the magnetic field and the location of the same with respect to the strings of the guitar. Referring to Figure IV showing a successful embodiment of my invention, it will be seen that I have provided a plurality of flat permanent magnets 25 and 25 with the north pole at the top side and the south pole at the bottom in each case These two magnets and 25 are particularly spaced apart as indicated at 21, and in order to satisfactorily assemble the mechanism, a suitable spacer 28 of non-magnetic material is inserted be tween the magnets 25 and 25. These magnets 25 and 26 are secured to and supported by a base member 39 of U-shaped in cross section, as indicated in Figure V having the side upwardly extending side walls and 32. This base is made of soft iron and forms a magnetic path cooperating with the magnets 25 and 28 so as to, in effect, bring the south pole up to a plane adjacent the top of the magnets or opposite the north pole, but spaced therefrom on either side and around the ends. Within the space between the magnets 25 and 28 of the upturned arms 3i and 32 of the base is located a winding 35 of a relatively large number of turns of wires which is connected to the wire 2| and hence tothe amplifier.

Overlying one of the permanent magnets 25 is a soft iron pole piece 3?, which I make narrower than the width of the magnet and also of such length as to extend over the edge thereof as indi" cated at 38 for purposes as will hereinafter be set forth. Over the other magnet 2'! is also located a soft iron pole piece 49 of the shape indicated having a narrowed extended tongue 4| likewise for purposes more fully hereinafter set forth.

To further improve the uniformity of the amplification produced by my device, over the space 23 between the two magnets Eli and E9 is a soft iron blanking or flux conducting strip 55 having (in the particular embodiment I have here made), legs 48 and 1'! to fit outside the coil 35 as indicated in Figure V. It will be also noted that the thickness of the blanking strip is substantially equal to that of the pole pieces iii and t!) so as to make the over all top surface of the pick up 28 substantially uniform throughout.

I provide a top cover 4-8 adapted to fit over the pick up mechanism thus far described, the cover it being of non-magnetic material, and in the particular embodiment herein illustrated has a transverse slot 49 therein for purposes as will hereinafter be set forth.

I also provide a pair of felt pads 53 secured to the bottom 3i so that the pick up may be applied to the equator without marring the surface of the instrument.

In Figures II and IV, I have shown the pick up 2%) in its relation to the strings of the guitar which I have numbered i, 2, 3, 3, 5., and Gas these strings are usually thus referred to in musical nomenclature. Attention is called to the fact that in musical instruments of this kind, the number 2 string of the treble set is the relatively heavy string as is intended to be shown in Figure IV so that with ordinary electrical pick up devices the tones produced by this string are unduly amplified. By my invention it will be noted from Figure IV, particularly, that this second string 2 comes opposite the space 2? between the two magnets Miami 2%. From this it will be understood that this string 2 is more or less outside the magnetic field produced by either of the magnets 25 and 26. On the other hand, strings 3, 3, ii, and ii in an instrument of this kind are such as to produce a more or less uniform amplification requiring no further modification of the sound produced by the magnet particularly with the pole piece 3'? and extended end 38. The number I string is a very fine string, and it will be noted-from Figure II that this comes opposite the slot id, which I provide in, the cover of the device was to aid in producing the correct volume to the amplification derived from the number i string. It will be also noted that the blanking soft iron blanking piece is located the space 2? between the magnets 25 and 26, and this, I have discovered, is important in connection with the use'of the device in amplifying the tones produced from the other strings. This prevents the winding 35 from picking up and receiving an induced current from the number 2 string to the extent that it otherwise would in case the strip M were omitted.

Referring to Figure III, it will seen that I have made the overall length of the pick up shorter by reason of providing extension 38.

on the pole piece 3'! which aids in the pickv up for the number 5 String since extension 38 comes under string 6 and the tongue S-i on the soft iron pole piece lli is important in the pick up for number i string. In each case, it will be noted that a minimum amount of shielding from the coil effected by reason of the particular configuration of pole 31; the extension 38; the shape of pole tongue ii.

Referring to Figure III further important feature of my assembly resides in the fact that the soft iron pole piece 4? is spaced as indicated at iii from the blanking strip 45 and the pole piece it is likewise spaced as indicated at 52 from said blanking strip in order to insure maintenance of the several fields of magnetic flux as produced by the separated magnets 25 and 26 as heretofore referred to.

Referring to Figure II, it will be seen that I have secured to the base of the pick up an attaching foot ti t adapted to be screwed on the underside of the pick guard if; as indicated in dotted lines, Figure I.

In Figure VI, I have shown a modification in which the two part magnet 25 and 26 and separation gap 2? are illustrated as connected together or made in one piece as designated at 25' and 2E with a transverse separating kerf or groove as shown. The magnets shown in Figure VI are then assembled as in the other embodiment shown in Figures II to V.

It is apparent that, within the scope of the invention, modifications and diiierent arrangements may be made other than is herein disclosed, and the present disclosure is illustrative merely, the invention comprehending all variations thereof.

What I claim is:

1. In an electromagnetic pick up device, said pickup adapted to fit between the strings and casing of a musical instrument and including a thin, oblong shaped casing having an open, boxlike base portion and a top cover portion, the core of said electromagnetic device comprising a hat elongated magnet, magnetized from one flat face as one pole to the other fiat face as the other pole, a juxtaposed section of non-magnetic material and a second piece of elongated magnetic material positioned at right angles to said firstmentioned magnet, said sections forming a thin transversely magnetized core of compact construction; a winding consisting of a large number of turns of conductive wire surrounding said three elements of said core binding the same in correlative position, said winding being located between said core and the walls of said box-like base, said base forming one of the pole pieces of said magnets; the other pole including two metal pieces, including one fiat elongated section of metal extending over one end of said windings and said first mentioned elongated magnetic material of said core; and another pole piece located over said last mentioned magnet and having a tongue extending over the other end portion of said winding said top cover being of magnetically impermeable material and having 9, depending flange closely fitting over the side walls of said bottom box-like base portion of said casing to retain the parts in assembled position.

2. In an electromagnetic pick up device, said pick up adapted to fit between the strings and easing of a musical instrument and including a thin, flat casing having two telescoping box-like open base and top portions, the core of said electromagnetic device comprising a flat elongated magnet, magnetized from one flat face as one pole to the other flat face as the other pole, a juxtaposed section of non-magnetic material and second piece of elongated magnetic material spaced from said first mentioned magnet, said sections forming a thin transversely magnetized core of the compact construction; a winding consisting of a large number of turns of conductive wire surrounding said three elements of said core binding the same in correlative position, said winding being located between said core and the walls of said box-like base, said base forming one of the pole pieces of said magnets; the other pole piece including a flat elongated section of metal extending over one end of said windings and said first mentioned elongated magnetic material of said core; and another pole piece located over said last mentioned magnet and having a tongue extending over the other end portion of said winding, a fiat metallic flux conducting strip over said middle section of non-magnetic material, said strip located between said top poles and of substantially the same thickness thereof; said top cover composed of magnetically impermeable material having depending flange closely fitting over the side walls of said base portion of said casing to retain the parts in assembled position.

3. In an electromagnetic pick up device, said pick up adapted to fit between the strings and casing-f a musical instrument and including a thin laterally extended casing having two telescoping box like open base and top portions, one end of said casing being enlarged to receive the leads to the amplifier, said ends squared off to position the device against the pick guard of a guitar, the core of said electromagnetic device including a flat elongated permanent magnet; a juxtaposed section of non-magnetizable material; and a second permanent magnet spaced from said first mentioned magnet, both of said magnets being magnetized from one fiat face as one pole to the other fiat face as the other pole, said sec-.

tions forming a thin transversely magnetized core of compact construction; a, winding consisting of a. large number of turns of conductive wire surrounding said three elements of said core binding the same in correlative position, said winding being located between said core and the walls of said box-like base, said base forming one of the pole pieces of said magnets; the other pole piece including a flat elongated section of v metal extending over one end of said windings and said first mentioned elongated magnet of said core; and another pole piece located over said last mentioned magnet and having a tongue extending over the end portion of said winding, a fiat U-shaped transverse strip of flux conducting material over said middle core section, the depending ends of said strip located between the winding and the inside casing side walls to retain the strip in place, said top cover being of non-magnetic material and having a depending flange closely fitting over the side walls of said base portion of said casing to retain the parts in assembled position.

HARRY DE ARMOND.

REFERENCES CITED The following references are of record in the file of this patent:

25,493 Australia, Sept. 2, 1936 

